Use of silane-functional polyvinyl alcohols in priming agents for separating papers and films

ABSTRACT

Release films or papers with improved properties are prepared by employing a binder which is a partly or fully hydrolyzed silane-group-containing polyvinyl alcohol polymer derived from a vinyl ester polymer containing 1-alkylvinylester moieties.

The invention relates to the use of silane-functional polyvinyl alcoholsin priming agents (primers) for separating (release) papers and films.

Release papers having dehesive properties with respect to adhesives areproduced by furnishing the paper backings with a silicone layer. Thesilicone layer is improved, particularly with the aim of preventingpenetration into the backing material during coating, by providing thebacking paper with a primer prior to application of the silicone layer.

From DE-A 3727078 it is known to use solutions of metal complexes andfilm formers such as polyvinyl alcohol as primer. In DE-A 4425737 awaterglass coat is formed on the paper as a primer. In the process ofEP-A 396789 the primer applied comprises a suspension comprisingfilm-forming substances, white pigment and noble-metal catalyst. DE-A19512663 recommends a pigment coat with aluminum hydroxide. Priming inEP-A 399079 is carried out by applying organosilanes or organosiloxanes,alone or in a mixture with binders such as polyvinyl alcohol. U.S. Pat.No. 5,358,977 describes the use of crosslinkable aromatic or aliphaticsubstances as primers. JP-A 58/214596 describes paper coated withsilane-modified polyvinyl alcohol that is suitable for producing releasepaper.

Disadvantageous features of the primer systems employed to date includetheir frequently unsatisfactory binding to the abhesive silicone layerand a resultant prolonged thermal-conditioning time for the crosslinkingsilicone, and also the unsatisfactory stability on storage.

An object which existed was therefore to provide a primer whicheliminates the abovementioned disadvantages and is suitable inparticular for producing release papers having a rapidly crosslinking,abhesive silicone coating.

The invention provides for the use of silane-functional polyvinylalcohols in primers for release papers and release films, comprising

at least one silane-containing polyvinyl alcohol based on fully orpartly hydrolyzed vinyl ester copolymers having a degree of hydrolysisof 75 to 100 mol %, obtainable by free-radical polymerization of

a) one or more vinyl esters of unbranched or branched alkylcarboxylicacids having 1 to 18 carbon atoms, of which a fraction of 1 to 30 mol %,based on total polymer, are one or more 1-alkylvinyl esters having alkylradicals having 1 to 6 carbon atoms, and of carboxylic acids having 1 to6 carbon atoms,

b) 0.01 to 10 mol % of one or more silane-containing, ethylenicallyunsaturated monomers, and, if desired,

c) further comonomers, copolymerizable therewith, and hydrolysis of theresultant polymers.

Suitable silane-containing polyvinyl alcohols are fully or partlyhydrolyzed vinyl ester polymers having a degree of hydrolysis of 75 to100 mol. The fully hydrolyzed vinyl ester polymers have a degree ofhydrolysis of preferably 97.5 to 100 mol %, more preferably 98 to 99.5mol %. The partially hydrolyzed polyvinyl esters have a degree ofhydrolysis of preferably 80 to 95 mol %, more preferably 86 to 90 mol %.The Hoppler viscosity (in accordance with DIN 53015 as a 4% by weightaqueous solution) serves as a measure of the molecular weight and of thedegree of polymerization of the partly or fully hydrolyzed, silanizedvinyl ester polymers, and is preferably from 2 to 50 mPas.

Suitable vinyl esters are vinyl esters of unbranched or branchedcarboxylic acids having 1 to 18 carbon atoms. Preferred vinyl esters arevinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate,vinyl laurate, vinyl pivalate and vinyl esters of α-branchedmonocarboxylic acids having 5 to 13 carbon atom, examples beingVeoVa9^(R) or VeoVa10^(R) (trade names of Shell). Vinyl acetate isparticularly preferred.

The fraction of 1-alkyl vinyl esters is 1 to 30 mol %, based on totalpolymer. Preference is given to 1-alkylvinyl esters having alkylradicals having 1 to 6 carbon atoms and formed from carboxylic acidshaving 1 to 6 carbon atoms, such as 1-methylvinyl acetate, 1-ethylvinylacetate, and 1-propylvinyl acetate. In one particularly preferredembodiment 1-methylvinyl acetate is copolymerized.

Suitable ethylenically unsaturated, silane-containing monomers b) areethylenically unsaturated silicon compounds of the general formula (I)R¹SiR² ₀₋₂(OR³)₁₋₃, where the definition of R¹ is CH₂⊚CR⁴—(CH₂)₀₋₃ orCH₂═CR⁴CO₂ (CH₂)₁₋₃, R² has the definition C₁ to C₃ alkyl radical,preferably methyl or ethyl, C₁ to C₃ alkoxy radical, preferably methoxyor ethoxy, or halogen, preferably Cl or Br, R³ is an unbranched orbranched, unsubstituted or substituted alkyl radical having 1 to 12carbon atoms, preferably 1 to 3 carbon atoms, such as methyl or ethyl,or is an acyl radical having 2 to 12 carbon atoms, it being possible ifdesired for R³ to be interrupted by an ether group, and R⁴ stands for Hor CH₃.

Suitable ethylenically unsaturated, silane-containing monomers b) arealso meth(acrylamides) containing silane groups, of the general formula(II) CH₂=CR⁵-CO—NR⁶—R⁷—SiR⁸ _(m)—(R⁹)_(3-m), where m=0 to 2, R⁵ iseither H or a methyl group, R⁶ is H or an alkyl group having 1 to 5carbon atoms; R⁷ is an alkylene group having 1 to 5 carbon atoms or adivalent organic group in which the carbon chain is interrupted by an 0or N atom, R⁸ is an alkyl group having 1 to 5 carbon atoms, and R⁹ is analkoxy group having 1 to 40 carbon atoms, which may be substituted byfurther heterocycles. In monomers in which two or more R⁵ or R⁹ groupsoccur these groups may be identical or different.

Examples of (meth)acrylamido-alkylsilanes of this kind are:

3-(meth)acrylamido-propyltrimethoxysilanes,3-(meth)-acrylamido-propyltriethoxysilanes,3-(meth)acrylamido-propyltri(β-methoxyethoxy)silanes,2-(meth)acrylamido-2-methylpropyltrimethoxysilanes,2-(meth)acrylamido-2-methylethyltrimethoxysilanes,N-(2-(meth)acrylamido-ethyl)aminopropyltrimethoxysilanes,3-(meth)acrylamido-propyltriacetoxysilanes,2-(meth)acrylamido-ethyltri-methoxysilanes,1-(meth)acrylamido-methyltrimethoxy-silanes,3-(meth)acrylamido-propylmethyldimethoxy-silanes,3-(meth)acrylamido-propyldimethylmethoxy-silanes,3-(N-methyl-(meth)acrylamido)-propyltrimethoxysilanes,3-((meth)acrylamido-methoxy)-3-hydroxy-propyltrimethoxysilanes.3-((meth)acrylamido-methoxy)-propyltrimethoxysilanes,N,N-dimethyl-N-trimethoxy-silylpropyl-3-(meth)acrylamido-propylammoniumchloride andN,N-dimethyl-N-trimethoxysilylpropyl-2-(meth)acryl-amido-2-methylpropylammoniumchloride.

Preferred ethylenically unsaturated, silane-containing monomers b) areγ-acryloyl- and γ-methacryloyloxy-propyltri(alkoxy)silanes,α-methacryloyloxymethyltri-(alkoxy)silanes,γ-methacryloyloxypropylmethyldi-(alkoxy)silanes; vinyl silanes such asvinyl-alkyldi(alkoxy)silanes and vinyltri(alkoxy)silanes, examples ofalkoxy groups which can be used including methoxy, ethoxy,methoxyethylene ethoxyethylene, methoxypropylene glycol ether and/orethoxypropylene glycol ether radicals. Examples of preferredsilane-containing monomers are 3-methacryloyloxypropyl-trimethoxysilane,3-methacryloyloxypropylmethyldimethoxysilane, vinyltrimethoxysilane,vinylmethyldimethoxysilane, vinyltriethoxysilane,vinylmethyldiethoxysilane, vinyltripropoxysilane,vinyltriisopropoxysilane, vinyltris(1-methoxy)isopropoxysilane,vinyltributoxysilane, vinyltriacetoxysilane,meth-acryloyloxymethyltrimethoxysilane,3-methacryloyloxy-propyltris(2-methoxyethoxy)silane,vinyltrichlorosilane, vinylmethyldichlorosilane,vinyltris(2-methoxyethoxy)silane, trisacetoxyvinylsilane,allylvinyltrimethoxysilane, allyltriacetoxysilane,vinyldimethylmethoxysilane, vinyldimethylethoxysilane,vinylmethyldiacetoxysilane, vinyldimethylacetoxysilane,vinylisobutyldimethoxysilane, vinyltriisopropyloxysilane,vinyltributoxysilane, vinyltrihexyloxysilane,vinylmethoxydihexoxysilane, vinyltrioctyloxysilane,vinyldimethoxyoctyloxysilane, vinylmethoxydioctyloxysilane,vinylmethoxydilauryloxysilane, vinyldimethoxylauryloxysilane and alsopolyethylene glycol-modified vinyl silanes.

Most-preferred silanes b) are vinyltrimethoxysilane,vinylmethyldimethoxysilane, vinyltriethoxysilane,vinylmethyldiethoxysilane, vinyltris(1-methoxy)isopropoxysilane,methacryloyloxypropyltris(2-methoxyethoxy)silane,3-methacryloyloxypropyltrimethoxysilane,3-methacryloyloxypropylmethyldimethoxysilane andmethacryloyloxymethyltrimethoxysilane, and mixtures thereof. The silanesb) are copolymerized preferably in an amount of 0.01 to 10.0 mol %, morepreferably 0.01 to 1.5 mol % of ethylenically unsaturated,silane-containing monomers.

Besides the silane-containing monomers it is also possible for one ormore further comonomers c) to be present, in a fraction of preferably0.1 to 25 mol %. By way of example, ethylene, propylene, isobutylene,butadiene, isoprene, chloroprene, styrene, α-methyl-styrene, vinylchloride, vinylidene chloride, vinyl fluoride, acrylonitrile,methacrylonitrile; alkyl vinyl ethers such as ethyl vinyl ether,n-butylvinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether,cyclohexyl vinyl. ether, octadecyl vinyl ether, hydroxybutyl vinylether, cyclohexanedimethanol monovinyl ether; vinyl methyl ketone,N-vinylformamide, N-vinyl-N-methylacetamide, N-vinylcaprolactam,N-vinyl-pyrrolidone, N-vinylimidazole. Also suitable are acrylic acidand methacrylic acid and also their esters and amides, such as methyl(meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl(meth)acrylate, ethylhexyl (meth)acrylate, benzyl (meth)acrylate,2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, n-hexyl(meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, lauryl(meth)acrylate, methoxyethyl (meth)acrylate, phenoxyethyl(meth)acrylate, isobornyl (meth)acrylate, stearyl (meth)acrylate,cyclohexyl (meth)acrylate, α-chloroacrylic esters, α-cyanoacrylicesters. Further examples are vinylcarbazole, vinylidene cyanide, vinylesters, acrylic anhydride, maleic anhydride, maleic and fumaric esters,monomers modified with sulfonic acid, such as2-acrylamido-2-methylpropanesulfonic acid, and their alkali metal salts,cationic monomers such astrimethyl-3-(1-(meth)acrylamide-1,1-dimethylpropyl)-ammonium chloride,trimethyl-3-(1-(meth)acrylamidopropyl)ammonium chloride,1-vinyl-2-methylimidazole and the quaternized compounds thereof.

The silane-containing vinyl ester polymers can be prepared in a knownway by means of polymerization; preferably by means of bulkpolymerization, emulsion polymerization, suspension polymerization or bypolymerization in organic solvents, more preferably in alcoholicsolution. The molecular weight can be adjusted in a manner known to theskilled worker by carrying out polymerization in the presence ofmolecular weight regulators. The silane-containing vinyl ester polymersare hydrolyzed in a manner known per se, for example by the belt orextruder method or in a stirred tank, in the alkaline or acidic range,with addition of acid or base. After the conclusion of the hydrolysisthe solvent is removed by distillation and the silane-containingpolyvinyl alcohol is obtained as a powder. The aqueous solution of thesilane-containing polyvinyl alcohols can also, where appropriate, bespray-dried and the silane-containing polyvinyl alcohol recovered as apowder. The preparation of pulverulent, silane-containing polyvinylalcohols is described in detail, for example, in DE-A 10232666. Commondrying methods are fluid-bed drying, thin-film drying, freeze drying andspray drying.

The primer composition may where appropriate further comprise additionalbinders and additives. Typical additional additives and binders includethe following: pigments, polyvinyl alcohols, carboxymethylcelluloses,starch, starch derivatives, alginates, proteins, aqueous polymerdispersions based on (meth)acrylic acid, (meth)acrylic esters,acrylonitrile, vinyl acetate, butadiene, styrene, and also plasticizerssuch as ethylene glycols, glycerol, and catalysts.

The primer composition can be applied in any desired way which issuitable for producing coatings from liquid materials and which is knownin many instances, such as by dipping, brushing, pouring, spraying,rolling or printing, for example, by means of an offset gravure coatingapparatus, for example, by blade or knife coating or by means of anairbrush. Application takes place preferably in an amount of 0.5 to 5.0g/m², more preferably 1.5 to 3.5 g/m².

The processes and formulas for the release coating of release papers andrelease films are known to the skilled worker. Suitable backings arepapers, especially base papers, and also films such as polyethylenefilms, PET films, nonwovens, wovens, and base crepe release stock. Afterthe backing material has been primed the silicone coat is applied usingthe stated application methods. Suitable silicone polymers havingdehesive properties are known to the skilled worker, and encompass, forexample, catenary dimethylpolysiloxanes having terminal hydroxyl groups,which on exposure to elevated temperature and in the presence oforganotin salt catalysts are condensed with silicic esters, or areobtained by the addition crosslinking route, by reacting catenarypolymers having vinyl end groups with hydropolysiloxanes with exposureto temperature in the presence of platinum catalysts. The formulas forthe silicone coat may where appropriate also comprise further additives,examples being film-forming assistants such as polyvinyl alcohol,carboxymethylcelluloses, or plasticizers such as ethylene glycol andglycerol.

EXAMPLES Example 1

A thermostatted laboratory apparatus with a capacity of 2.5 liters wascharged under nitrogen with 612 g of water, 61.2 mg of copper(II)acetate and 61.2 g of a 5% strength solution of polyvinylpyrrolidone(PVP-K90) in water.

With stirring a solution of 620 mg of t-butyl per-2-ethylhexanoate(TBPEH, 99% in water), 322 mg of t-butyl perneodecanoate (Pergan PND,95% in water), 4.9 g of vinyltriethoxysilane, 48.9 g of isopropenylacetate and 42.8 g of isopropanol in 612 g of vinyl acetate was run in.The reactor was heated to 51.5° C., and after the reaction had subsidedheating was carried out in stages to 75° C. The system was held at thistemperature for a further 2 hours and then cooled. The resulting beadsof polymer were filtered off with suction, washed thoroughly with waterand dried.

In a laboratory reactor with a capacity of 2.5 liters, 90 g of polymerbeads were dissolved in 810 g of methanol at 50° C. The solution wascooled to 30° C, 500 g of methanol were overlaid on the solution withthe stirrer switched off, and immediately thereafter methanolic NaOH wasadded (10 g of NaOH, in 46% strength solution in water, in 90 g ofmethanol) and the stirrer was switched on.

The solution became increasingly more turbid. During the gel phase, thestirrer was set to a higher speed in order to comminute the gel. Afterthe gel phase, the reaction was allowed to continue for 2 hours more,after which the mixture was neutralized with acetic acid and the solidform was filtered off, washed and dried. This gave a fully hydrolyzedpolyvinyl alcohol having a Höppler viscosity of 28 mPas (4% in water).

Comparative Example 1

Fully hydrolyzed polyvinyl alcohol containing vinyl-silane units andhaving a Hoppler viscosity of 25 mPas (4% in water).

Comparative Example 2

Fully hydrolyzed polyvinyl alcohol containing no silane and having aHoppler viscosity of 25 mPas (4% in water).

Production of the Paper

The primers from the inventive and comparative examples were eachapplied to a base paper, using a laboratory sizing press, and driedappropriately (coating 1.5 g/m² to 3 g/m²). The paper thus primed hadapplied to it a release coat comprising 100 parts by weight of avinyl-terminated polysiloxane (Dehesive 920), 2.4 parts by weight of anH-containing siloxane (crosslinker V90) and 1 part by weight of Ptcatalyst (catalyst OL), and the coated paper was thermally conditionedat 150° C. for 7 seconds.

Description of the Test Methods Migration

A test adhesive tape was applied to the freshly siliconized face andthen peeled off again. The adhesive strip was folded together so thatthe adhesive surfaces were in contact. Then the ends were pulled apart(loop test). If the layers adhering to one another have good adhesion,this suggests good adhesion of the silicone coat on the substrate. Bothtests are scored in school grades from 1 to 6:1=very good, 6=very poor

Ruboff

The siliconized surface is rubbed once, vigorously, with the finger, andthe rubbed area is viewed under obliquely incident light. If there aredifferences in lightness, or streaks, in this area, the adhesion of thesilicone product is not optimum. In addition, the silicone coat isrubbed strongly with the finger a number of times and the amount ofabraded particles is observed. Both tests are scored in school gradesfrom 1 to 6. Test results: Comp. Comp. Comp. Comp. Ex. 1 ex. 1 ex. 2 Ex.1 ex. 1 ex. 2 Storage 0 0 0 7 d 7 d 7 d time Migration 1 1 4 1 5 5Ruboff 1 1 4 1 5 6

The test shows the superiority of the silane-containing polyvinylalcohols, used in accordance with the invention, after storage.

Determination of the storage stability of 11% strength aqueous solutionsof the modified polyvinyl alcohols at pH=8.5: Höppler viscosity Höpplerviscosity [mPas] [mPas] Storage time Example 1 Comparative example 1immediately 28.1 25.1  1 day 28.1 27.8  2 days 28.1 31.4  3 days 28.235.8  5 days 28.2 42.9  7 days 28.2 61.7 14 days 28.3 90.5

The test shows that the silane-containing polyvinyl alcohols used inaccordance with the invention show no increase in viscosity duringstorage.

1-7. (canceled)
 8. In a process for the preparation of release films andcoatings on a substrate by applying a primer to the substrate and thenapplying a silicone release coating, the improvement comprising,selecting as a primer, at least one silane-containing polyvinyl alcoholderived from fully or partly hydrolyzed vinyl ester copolymers having adegree of hydrolysis of 75 to 100 mol %, obtained by free-radicalpolymerization of a) one or more vinyl esters of unbranched or branchedalkylcarboxylic acids having 1 to 18 carbon atoms, of which a fractionof 1 to 30 mol %, based on total polymer, are one or more 1-alkylvinylesters of carboxylic acids having 1 to 6 carbon atoms, wherein the alkylradicals have 1 to 6 carbon atoms, b) 0.01 to 10 mol % of one or moresilane-containing, ethylenically unsaturated monomers, and, optionally,c) further comonomers copolymerizable therewith, and hydrolyzing theresultant polymers.
 9. The process of claim 8, wherein thesilane-containing polyvinyl ester copolymer is a copolymer of vinylacetate.
 10. The process of claim 8, wherein said 1-alkylvinyl estersare selected from the group consisting of 1-methylvinyl acetate,1-ethylvinyl acetate, and 1-propylvinyl acetate, and mixtures thereof.11. The process of claim 8, wherein the silane-containing polyvinylalcohol is obtained by copolymerizing one or more ethylenicallyunsaturated, silane-containing monomers selected from the groupconsisting of ethylenically unsaturated silicon compounds of the formula(I) R¹SiR² ₀₋₂(OR³)₁₋₃, where R¹ is CH₂═CR⁴—(CH₂)₀₋₃ orCH₂═CR⁴CO₂(CH₂)₁₋₃, R² is a C₁ to C₃ alkyl radical, C₁ to C₃ alkoxyradical, or halogen, R³ is an unbranched or branched, unsubstituted orsubstituted alkyl radical having 1 to 12 carbon atoms, or is an acylradical having 2 to 12 carbon atoms, R³ optionally interrupted by anether group, and R⁴ is H or CH₃, and meth(acrylamides) containing silanegroups, of the formula (II) CH₂═CR⁵—CO—NR⁶—R⁷—SiR⁸ _(m)—(R⁹)_(3-m),where m=0 to 2, R⁵ independently is H or a methyl group, R⁶ is H or analkyl group having 1 to 5 carbon atoms, R⁷ is an alkylene group having 1to 5 carbon atoms or a divalent organic group in which the carbon chainis interrupted by an O or N atom, R⁸ is an alkyl group having 1 to 5carbon atoms, and R⁹ is an alkoxy group having 1 to 40 carbon atoms,optionally substituted by heterocycles.
 12. The process of claim 11,wherein the silane-containing polyvinyl alcohol is obtained bycopolymerizing one or more ethylenically unsaturated, silane-containingmonomers selected from the group consisting of γ-acryloyl- andγ-methacryloyl-oxypropyltri(alkoxy)silanes,α-methacryloyloxymethyltri(alkoxy)silanes,γ-methacryloyloxypropylmethyldi(alkoxy)silanes,vinylalkyldi(alkoxy)silanes, and vinyltri(alkoxy)silanes.
 13. Theprocess of claim 12, wherein at least one alkoxy group is selected fromthe group consisting of methoxy, ethoxy, methoxyethyleneoxyethoxyethyleneoxy, methoxypropyleneoxy and ethoxypropyleneoxy radicals.14. The process of claim 8, wherein 0.01 to 1.5 mol % of ethylenicallyunsaturated, silane-containing monomers are copolymerized.
 15. A releasefilm or paper, comprising: a substrate, a primer coat applied to thesubstrate, and a silicone release coating applied over the primer,wherein the primer comprises a primer of claim
 8. 16. A release film orpaper comprising a substrate, a primer coat applied to the substrate,and a silicone release coating applied over the primer, wherein theprimer comprises at least one silane-containing polyvinyl alcoholderived from fully or partly hydrolyzed vinyl ester copolymers having adegree of hydrolysis of 75 to 100 mol %, obtained by free-radicalpolymerization of a) one or more vinyl esters of unbranched or branchedalkylcarboxylic acids having 1 to 18 carbon atoms, of which a fractionof 1 to 30 mol %, based on total polymer, are one or more 1-alkylvinylesters of carboxylic acids having 1 to 6 carbon atoms, wherein the alkylradicals have 1 to 6 carbon atoms, b) 0.01 to 10 mol % of one or moresilane-containing, ethylenically unsaturated monomers, and, optionally,c) further comonomers copolymerizable therewith, and hydrolyzing theresultant polymers.